No surprise — those Facebook photos of your friends on vacation or celebrating a birthday party can make you feel lousy.

Facebook is supposed to envelope us in the warm embrace of our social network, and scanning friends’ pages is supposed to make us feel loved, supported and important (at least in the lives of those we like). But skimming through photos of friends’ life successes can trigger feelings of envy, misery and loneliness as well, according to researchers from two German universities. The scientists studied 600 people who logged time on the social network and discovered that one in three felt worse after visiting the site—especially if they viewed vacation photos. Facebook frequenters who spent time on the site without posting their own content were also more likely to feel dissatisfied.

“We were surprised by how many people have a negative experience from Facebook with envy leaving them feeling lonely, frustrated or angry,” study author Hanna Krasnova from the Institute of Information Systems at Berlin’s Humboldt University told Reuters. “From our observations some of these people will then leave Facebook or at least reduce their use of the site.”

The most common cause of Facebook frustration came from users comparing themselves socially to their peers, while the second most common source of dissatisfaction was “lack of attention” from having fewer comments, likes and general feedback compared to friends.

The study authors note that both men and women feel pressure to portray themselves in the best light to their Facebook friends, but men are more likely to post more self-promotional content in their “About Me” and “Notes” sections than women, although women are more likely to stress their physical attractiveness and sociability.

Overall, however, shared content does not have to be “explicitly boastful” for envy feelings to emerge. In fact, a lonely user might envy numerous birthday wishes his more sociable peer receives on his FB Wall. Equally, a friend’s change in the relationship status from “single” to “in a relationship” might cause emotional havoc for someone undergoing a painful breakup.

So far, it seems that the positive effects of being socially connected supersede the negative consequences of feeling inferior or left out by your circle of friends. But the authors suggest that if the hurtful feelings grow, Facebook and other social media may no longer be a fun way to stay connected with friends, but could become just another source of stress for people.

The research will be presented at an information system conference in Germany in February, called the 11th International Conference on Wirtschaftsinformatik.